The invention relates to a heel unit for a safety ski binding, comprising a base body intended to be fixed to a ski, a return cam rotatably mounted on the base body about an axis and returned by a spring device into a rotary starting position, a sole holder rotatably mounted about the same axis, and a unidirectional blocking arrangement arranged between the return cam and the sole holder and comprising at least one blocking arrangement, said blocking arrangement being blocked in the opening direction and being releasable against a slide spring force by means of a manual release lever.
Heel units of this kind can be opened for example by means of a manual actuation lever with a minimum effort, by firstly decoupling the sole holder from the spring arrangement which normally urges the sole holder in the closing direction. During such a manual release process, the sole holder can thereby be pivoted into the opening position without having to overcome for this purpose the relatively high return force exerted by the spring arrangement. As soon as the heel unit is closed again and the forced closure is again established between the sole holder and the spring-urged return cam, the heel unit fulfills again the usual holding function and simultaneously allows a reliable safety release.
In a heel unit known from DE 26 28 748 A1, a snap member urged by the spring arrangement engages a slide rail provided with a culminating point, the slide rail being provided on a swing arm concentric to the sole holder. In a starting rotary position corresponding to the closing position, the swing arm and the sole holder contact each other along a circular path eccentric with respect to the pivot axis. A ball lock provided on the swing arm is active between the latter and the sole holder, and locks when the sole holder is urged in the opening direction, provided that the sole holder has already reached its starting rotary position with respect to the swing arm. The ball lock can be released by means of a manual actuation lever.
The drawback of these known heel units is the forced closure necessary between the swing arm and the sole holder for holding the sole until the safety release can no longer be ensured for even small displacements of the starting relative rotary position of these two components of the heel unit. In other words, the ball lock does not block anymore because of the distance which appears between the swing arm and the counter-surface provided on the sole holder. This distance increases as a function of the actual variation of the starting relative rotary position. Consequently, if the sole holder is not completely downwardly engaged, for example because of the formation of ice on the surface of the ski or because of an over-standard sole thickness, it can happen that the required blocking is not guaranteed.